Modern aircraft have a plurality of control surfaces, systems, actuators, torques, temperatures, and the like which need to be monitored to ensure proper operation of the aircraft. In order to be able to monitor the various aircraft parameters, sensors are used on the individual control surfaces, actuators, and engines to detect the various parameters. The values detected by the sensors can subsequently be employed for instrumentation, used to generate control commands, and for various diagnostics. With diagnostic applications, the values detected by the sensors may be compared with predetermined values for a given parameter under selected conditions and a malfunction can be identified in the event a deviation is detected by the respective sensor from the predetermined values.
A variety of sensors and actuators may be employed depending on the application. Sensors such as rotary or Linear Variable Differential Transformer sensors (RVDT or LVDT sensors), synchros and resolvers are conventionally used as sensors in aircraft because they are very robust with respect to external disturbances and have simple construction. However, in other applications, potentiometers and some low-level sensors are also commonly employed. Likewise, actuators may include valves, solenoids, relays, motors, brakes, and the like.
When sensors are used to detect various aircraft parameters, the sensors used must typically be monitored to ensure error free operation. Failures of sensors, and/or the wiring harness, or controller interfaces to sensors impact system reliability and result in a need for redundancy and overdesign to ensure operation. It is also desirable to ensure that potential failures are not only detectable, but also, preferably relegated to lesser importance and minimized impact on system reliability. Similarly, actuators are employed to move controls, control surfaces and the like to manipulate and control aircraft parameters, therefore commonly is it also desirable to monitor the operation of actuators to ensure error free operation. Failures of actuators and/or the wiring harness, or controller interfaces to them impact system reliability and result in a need for redundancy and overdesign to ensure operation. It is also desirable to ensure that potential failures are not only detectable, but also, preferably relegated to lesser importance and minimized impact on system reliability.
Some testing includes lightning protections. Qualification testing for lightning pin injection on sourced outputs permits use of an estimated ‘remote load impedance’, which is the equivalent impedance presented by the equipment between the load conductors and chassis (Earth) ground of the remote load. Furthermore, continued air-worthiness requirements dictate that lightning protection circuits should be testable, preferably by Built in Test (BIT), but at a minimum through component acceptance testing. Unfortunately, current BIT techniques do not have the capability to measure the remote load impedance, so taking advantage of its permitted use during qualification test or as part of a continued air-worthiness analysis is not available. Therefore, it is desirable to have a BIT capability that includes determination of remote load impedance where possible.